The overall objective of this component project is to understand batter the coding ofintensity in the tactile systems. The motivation for the experiments derive from three sources: Zwislocki's theory that the jnd is independent of the shape of the sensation magnitude function, that the integrity of the four-channel model persists and can be identified at the superthreshold levels of stimulation, and that our findings can be generalized to include both the auditory and tactile systems. The research plan is divided into four specific, but not mutually exclusive areas, those being: 1) channel specificity, 2) temporal parameters, 3) response variability and 4) interactions between pain and taction. Specific experiments include measurements of the jnd within each of the four tactile channels; the effects of temperature, contractor indentation, and the use of a surround of the jnd; to test further the independence of the jnd from the shape of the sensation magnitude function when sensation magnitude is held constant; the source of discontinuities in the subjective-magnitude functions, the effects of variation temporal parameters on the jnd and procedures using pedestal and test stimuli and testing the Zwislocki theory of intensity coding by the standard deviations of subjective-magnitude matches. Standard and proven psychophysical procedures will be used throughout, those being: 1) DL/JND; 2) Sensation Magnitude; 3) Masking and Adaption; 4) Temporal and Spatial Summation and 5) Thermally Induced Pain. The theoretical bases that drive all specific hypotheses are the four channel model of cutaneous mechanoreception and Zwislocki's theory of differential intensity sensitivity, developed under the aegis of this program project. Extensive modifications have been made to satisfy the concern of the sensory disorders and language review group.